Pilot study done in post-menopausal women with a history of estrogen-receptor positive breast cancer and specific apolipoprotein E phenotypes known to affect serum lipid levels, to determine the feasibility of doing a larger study looking at the relationship between diet lipid and fiber intake, apolipoprotein E phenotype and circulating serum estrogen levels, in women with a disease (breast cancer) known to be affected by estrogen. The outpatient study will be done in 6 women. For 2 to 4 weeks, the subjects will be fed a high fat, low fiber diet, and for 4-6 weeks the subjects will be fed a low fat, high fiber diet, with the intent of determining how many weeks are required before changes in circulating estrogen levels are seen. The study will utilize the GCRC for 8 months.